In a lithium secondary battery, materials allowing insertion and release of lithium ions are used as a cathode and an anode, and an organic electrolyte or a polymer electrolyte is charged between the cathode and the anode. When the lithium ions are inserted and released at the cathode and the anode, electrical energy is generated through oxidation and reduction reactions.
At present, carbonaceous materials are mainly used for the anode active material of a lithium secondary battery. However, in order to further improve the capacity of the lithium secondary battery, use of an electrode active material with a higher capacity is required.
To satisfy this requirement, metallic Si, Sn, etc., which exhibit higher charge-discharge capacity than the carbonaceous materials and are electrochemically alloyable with lithium, have been used as an electrode active material. However, these metallic electrode active materials tend to crack or pulverize because of severe volume change accompanied by charge and discharge of lithium. Accordingly, the capacity of a secondary battery using these metallic electrode active material declines rapidly with the progress of charge-discharge cycles and also the lifetime is reduced.
Thus, there has been an attempt to replace the metals such as Si, Sn, etc. with their oxides for use as an electrode active material, in order to reduce the cracking and pulverization problems. Although use of the metal oxide electrode active materials solves the problem, initial efficiency is lower as compared to the carbonaceous electrode active materials. Furthermore, during the initial reaction with lithium ions, an irreversible phase such as a lithium oxide or a lithium metal oxide is formed, resulting in further decline of initial efficiency than the metallic electrode active materials.